CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($)	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Cash Flows From Operating Activities
Net loss	$ (77,673,000)	$ (70,477,000)
Adjustments to reconcile net loss to cash used in operating activities:
Depreciation and amortization expense	20,923,000	13,397,000
Amortization of deferred contract acquisition costs	7,722,000	4,990,000
Stock-based compensation expense	25,012,000	26,285,000
Net accretion of discounts and amortization of premiums on available-for-sale securities	(1,137,000)	(78,000)
Deferred income taxes	0	7,000
Provision for bad debt	861,000	909,000
Change in fair value of redeemable convertible preferred stock warrant liability	1,517,000	1,187,000
Other	27,000	62,000
Changes in operating assets and liabilities, net of effect of acquisitions:
Accounts receivable, net	(7,911,000)	(15,269,000)
Contract assets	82,000	2,344,000
Deferred contract acquisition costs	(12,923,000)	(8,639,000)
Prepaid expenses and other current assets	(7,525,000)	(3,293,000)
Other noncurrent assets	(1,686,000)	(228,000)
Accounts payable	(994,000)	5,037,000
Accrued expenses and other current liabilities	5,652,000	5,065,000
Deferred revenue	13,614,000	5,263,000
Liability for early exercise of unvested stock options	0	19,000
Other noncurrent liabilities	4,096,000	2,408,000
Net cash used in operating activities	(30,343,000)	(31,011,000)
Cash Flows From Investing Activities
Purchases of property and equipment	(30,981,000)	(12,507,000)
Capitalized internal-use software	(11,332,000)	(5,645,000)
Purchases of available-for-sale securities	(157,075,000)	(87,115,000)
Sales of available-for-sale securities	1,978,000	0
Maturities of available-for-sale securities	132,398,000	42,955,000
Other investing activities	30,000	42,000
Net cash used in investing activities	(64,982,000)	(62,270,000)
Cash Flows From Financing Activities
Proceeds from issuance of preferred stock, net of issuance costs	0	149,975,000
Proceeds from initial public offering, net of underwriting discounts and commissions	570,544,000	0
Proceeds from the exercise of stock options	2,899,000	4,317,000
Proceeds from the early exercise of stock options	2,871,000	14,525,000
Repurchases of unvested common stock	(155,000)	(48,000)
Payments on note payable	(218,000)	(266,000)
Proceeds from build-to-suit lease financing obligation drawdown	58,000	107,000
Payments of deferred offering costs	(3,734,000)	0
Net cash provided by financing activities	572,265,000	168,610,000
Net increase in cash, cash equivalents, and restricted cash	476,940,000	75,329,000
Cash, cash equivalents, and restricted cash, beginning of period	31,426,000	26,881,000
Cash, cash equivalents, and restricted cash, end of period	508,366,000	102,210,000
Supplemental Disclosure of Cash Flow Information:
Cash paid for interest	573,000	572,000
Cash paid for taxes	2,027,000	2,149,000
Supplemental Disclosure of Non-cash Investing and Financing Activities:
Stock-based compensation capitalized for software development	1,428,000	183,000
Accounts payable and accrued expenses related to property and equipment additions	1,291,000	2,275,000
Vesting of early exercised stock options	2,389,000	813,000
Deferred offering costs, accrued but not paid	1,770,000	0
Conversion of redeemable convertible preferred stock to common stock	331,521,000	0
Conversion of redeemable convertible preferred stock warrant liability reclassified to additional paid-in capital	$ 3,135,000	$ 0